The present invention relates to respective methods for manufacturing conductive wafers, thin-plate sintered compacts and ceramic substrates for a thin-film magnetic head and to a method for machining conductive wafers.
In recent years, a thin-film magnetic head has been used for various types of magnetic recording devices such as a hard disk drive (HDD) and a floppy disk drive (FDD) for a computer. As a thin-film magnetic head has been downsized, the thickness of a wafer, used as a substrate for such a head, has also been reduced. Since a substrate for a magnetic head is required to have high hardness and high abrasion resistance, Al.sub.2 O.sub.3 --Ti, SiC and ZrO.sub.2 ceramics are currently used therefor. For example, an ALTIC wafer, widely used currently as a ceramic substrate for a magnetic head, is manufactured by sintering a powder green compact of raw materials such as alumina (Al.sub.2 O.sub.3) and titanium carbide (TiC). An ALTIC wafer having a thickness of about 1.2 mm is practically used today as a substrate for a magnetic head. In order to realize magnetic recording with even higher density, however, the development of an even thinner and further planarized ceramic substrate is awaited.
A sintering process is indispensable for manufacturing a ceramic substrate. However, in accordance with currently available techniques, a sintered ceramic substrate is often deformed, e.g., warped, during the sintering process. One of the main reasons is the non-uniform temperature distribution of the sintered compact during the sintering process. It is now known that the thinner the thickness of a ceramic substrate to be formed is (e.g., if the thickness is equal to or smaller than 2 mm), the more warped the substrate is likely to get. Conventionally, such a "warp" has been eliminated by planarizing the surface of a substrate through polishing.
A sintered compact used as a substrate for a thin-film magnetic head has extremely high hardness (the Vickers hardness thereof is 2,000 or more). Accordingly, it takes a very long time to polish such a sintered compact. For example, sometimes it takes several tens of hours to reduce the thickness of a plate sintered compact from 2 mm to 1.2 mm by polishing it. On the other hand, the thinner a sintered compact is, the less rigid and the more warped the sintered compact gets. Thus, if an even thinner ceramic substrate is required in the near future, the conventional method for forming a ceramic substrate will take an enormous amount of time to perform various post-sintering processes like polishing. Accordingly, it is expected that the productivity will drastically decrease in such a case. In other words, this problem constitutes a great obstacle to further increasing the productivity of a thin-film magnetic head.
It is noted that the "warp" problem is not unique to a ceramic substrate for a thin-film magnetic head, but possibly happens during the formation of any thin-plate sintered compact in general. Therefore, the above-described problems (that is, polishing for eliminating such a warp takes a lot of time and increases the manufacturing cost) are generally true of any method for manufacturing a sintered compact involving a sintering process (e.g., a method for manufacturing a sintered magnet).